New York City’s Department of Investigation is moving forward with a broad examination of how city officials handled information about environmental hazards following the September 11 attacks, including what successive mayoral administrations knew about toxic substances at and around Ground Zero. The investigation will cover the administrations of Rudy Giuliani, Michael Bloomberg, Bill de Blasio and Eric Adams.

The probe was ordered by the City Council in July 2025 through Resolution 560-A. The city has allocated $3.81 million over fiscal years 2026 and 2027 to support the investigation, which is expected to culminate in a public report.

The investigation comes as renewed attention is being focused on the city’s handling of air-quality concerns in the aftermath of 9/11. In September, the Mamdani administration released an initial collection of more than 170,000 pages of previously withheld records detailing the city’s response, environmental conditions and health concerns following the attacks. The records include the so-called Harding Memo and other documents concerning asbestos, air quality and the city’s response to residents and workers.

The historical record also includes the Environmental Protection Agency’s September 18, 2001 announcement that monitoring results indicated the public was not being exposed to excessive levels of asbestos or other harmful substances. EPA Administrator Christine Todd Whitman said at the time that she could reassure New Yorkers that the air was safe to breathe. A subsequent EPA Inspector General investigation concluded that the agency did not have sufficient data and analysis at the time to make such a broad determination.

Michael Barasch, an attorney who represents thousands of people affected by 9/11-related illnesses, has argued that the newly released records warrant a closer examination of what city officials knew and when they knew it. The investigation is intended to establish the facts surrounding the city’s knowledge, decision-making and response, rather than relying solely on accounts from individual officials or advocates.

The DOI’s review is expected to examine records spanning multiple administrations and ultimately provide the City Council and public with a detailed account of what city government knew about the environmental risks following the attacks and how that information was handled.